Electric heater assemblies

ABSTRACT

An electric strip heater of the so-called &#39;&#39;&#39;&#39;mica type&#39;&#39;&#39;&#39; comprises a a sheet metal channel with a mica sheet disposed in the channel flatwise against the base thereof. The terminals of the heater have thin flat heads and threaded shanks. The shanks pass through aligned openings at each end of (1) a flat mica resistor plate having a resistor wound therearound, (2) a mica cover plate overhanging the resistor plate and (3) a flat metal cover plate overlying the mica cover plate. A dish-shaped metal washer is disposed over the end of each terminal shank and is deformed by a pressing action in a direction toward the terminal head to provide a subassembly which is disposed within the metal channel with the flat terminal heads positioned against the mica sheet therein. The sides of the channel are pressed over the metal cover plate to complete the assembly. A nut is threaded on each terminal shank outwardly of the dished washer for securing an electrical conductor to the shank.

United States Patent [191 Cappell [451 Apr. 30, 1974 [541 ELECTRICHEATER ASSEMBLIES [75] Inventor: Charles W. Cappell, Allison Park,

[73] Assignee: Emerson Electric Co., St. Louis, Mo.

22 Filed: Jan. 16, 1973 i [21] Appl. No.: 324,064

219/541, 219/544, 219/551, 338/276, 338/301 [51] Int. Cl. H05b 3/30,HOlc H02 [58] Field of Search 219/528, 538, 541, 542,

[56] References Cited UNITED STATES PATENTS 2,797,296 6/1957 Fowler eta1 219/528 Boecher et al...

Trent Primary ExaminerA. Bartis Attorney, Agent, or Firm-MichaelWilliams ABSTRACT An electric strip heater of the so-called mica typecomprises a a sheet metal channel with a mica sheet disposed in thechannel flatwise against the base thereof. The terminals of the heaterhave thin flat heads and threaded shanks. The shanks pass throughaligned openings at each end of l) a flat mica resistor plate having aresistor wound therearound, (2) a mica cover plate overhanging theresistor plate and (3) a flat metal cover plate overlying the mica coverplate. A dish-shaped metal washer is disposed over the end of eachterminal shank and is deformed by a pressing action in a directiontoward the terminal head to provide a subassembly which is disposedwithin the metal channel with the flat terminal heads positioned againstthe mica sheet therein. The sides of the channel are pressed over themetal cover plate to complete the assembly. A nut is threaded on eachterminal shank outwardly of the dished washer for securing an electricalconductor to the shank.

3 Claim, 4 Drawing Figures 1 ELECTRICAL lNst/LATION PATENTED APR 30 m4SREU 1 0F 2 ELECTRlCAL SULANON ELECTRIC ASSEMBLIES BACKGROUND ANDSUMMARY Strip heaters, as previously manufactured, are shown incross-section in FIG. 4 of the drawings. The terminals are of specialmanufacture since they are required to provide an intermediate shoulderand a tubular end portion which has a plurality of longitudinal slits sothat the end portion may be upset. In the heater shown in FIG. 4,.onlythe mica plate which supports the resistor may be assembled with theterminals outside of the channel. Further, in final assembly with allother parts in the channel, the upset end portion of the terminalsfrequently had burrs which have a tendency to dig into the mica sheetwhich insulates the terminals from the channel base and sometimespunctured or fractured such sheet.

The present invention makes it possible to effect a complete subassemblyof parts outside of the channel so that the final assembly with thechannel is relatively simple. Further, the invention enables the use oflowcost terminals which require only a thin, flat head and a threadedshank. The flat heads provide a smooth, unbroken surface which maybepressed tightly against the mica sheet within the channel withoutpuncturing or fracturing the sheet.

Briefly, the invention comprises a sheet metal channel, with a firstmica sheet withinthe channel and disposed flatwise against the channelbase. A subassembly is independently formed' and includes superposedsecond and third mica sheets and a metal cover plate, all three partshaving aligned holes to respectively pass the shanks of tenninalmembers, each of which has a fiat head bearing against the outer surfaceof the second mica sheet. Securing means, in the form of a dishedwasher, is disposed over that part of each terminal shank which extendsoutwardly of the cover plate, and pressure is applied to both washers totend to flatten them and cause them to grip the terminal shanks. Thispressure also presses the mica sheets and cover plate in closeface-to-face engagement.

The second mica sheet has a resistor wound thereon, and'the third micasheet overhangs the second sheet so that when the sub-assembly is placedin the channel, the resistor is held spaced from the side walls of thechannel. The flat heads of the terminal members bear against the firstmica sheet. To complete the assembly, the free parts of the side wallsof the channel are bent over the cover plate.

DESCRIPTION OF THE DRAWINGS In the drawings accompanying thisspecification and forming-a part of this application, there is shown,for purpose of illustration, an embodiment which the invention mayassume, and in these drawings:

FIG. 1 is a separated, perspective view of parts included in thepreferred embodiment, 7

FIG. 2 is an enlarged, transverse sectional view through the terminalportion of a completed heater,

FIG. 3 is an enlarged, sectional view of a dish-shaped metal washer usedin the assembly, and

FIG. 4 is an enlarged, transverse sectional view through the terminalportion of a heater as previously manufactured.

DESCRIPTION OF THE PREFERRED EMBODIMENT With particular reference toFIG. 1, the' embodiment herein disclosed comprises a sheet metal channel10 having a flat base 11 and upstanding sides 12-12. A flat sheet 14 ofmica, or similar electrical insulating material, is adapted to bedisposed within the channel 10 and preferably is of a length and widthequal to that of the base 11.

Adapted to overlie the mica sheet 14 is a further flat sheet 15 of mica,or other suitable insulation material, which is of a length and widthless than that of the base 11 so that in final assembly it will be heldout of electrical contact with the latter. The sheet 15 has holes 16-16adjacent to the ends thereof, and a current resistor 17, either wire orribbon, is wound about the sheet 15 in a flat helix. Each end of theresistor is wound several times around the sheet 15, between an end hole16 and a side portion of the sheet, to provide the plurality of closelyspaced windings 18.

A terminal 19 is provided for each end of the resistor, each terminalhaving a thin, flat head 20 and a threaded shank 21. The head 20 isadapted to be clamped between the mica sheet 14 and the underside of theresistor sheet 15 and thus held in good electrical contact with theplural windings 18 adjacent to a respective hole 16. The threaded shank21 of each terminal fits closely through a respective hole 16 andelectrically engages the plural windings passing through the hole toprovide further electrical contact between the resistor 17 and theterminals.

Another flat sheet 23 of mica, or other suitable insulating material, isadapted to overlie the resistor sheet 15. The sheet 23 is about the samewidth and length as the mica sheet 14 and has end holes 24-24 which areabout the same size as the holes 16 so as to closely pass the shanks 21of respective terminals. Thus, the resistor sheet 15 is anchored betweenthe mica sheets 14 and 23 and cannot shift transversely relativethereto.

A flat metal cover 25 is adapted to overlie the mica sheet 23 and thiscover is about the length of the base 11 but just enough less in widthso that the channel sides 1212 may be closely bent thereover, as seen inFIG. 2. The metal cover 25 has end holes 2613 26-- which are largeenough to closely receive mica washers 27, each washer having a hole toclosely pass the shank 21 of a respective terminal 19. Thus, theterminals are electrically insulated from the metal cover.

Overlying the metal cover 25 and assembled on each terminal are a micawasher 28, a metal washer 29, a dished metal washer 30 (seen in enlargedsection in FIG. 3) and a metal washer 31, all of the foregoing washershaving holes to closely pass the shank 21 of a respective terminal 19. Anut 32 is adapted to be threaded on each terminal shank 21.

The preferred method of producing the assembly shown in enlarged sectionin FIG. 2 is to dispose the terminal shanks 21 through respective, holes16 in the resistor sheet 15 and through respective holes 24 in the micasheet 23. The mica washers 27 may be fitted on the extending portions ofthe terminal shanks 21 and the metal cover 25 disposed over the micasheet 23 with the mica washers 27 fitted with respective cover holes 26.It is also possible to first fit the mica washers within the cover holes26 and then dispose the cover 25 over the mica sheet 23.

Mica washers 28, metal washers 29, and dished washers 30 are thendisposed over the extending ends of the terminal shanks. By means ofsuitable pressing apparatus (not shown) pressure is applied downwardlyon each dished washer 30 to force the metal cover 25, the mica sheet 23and the resistor sheet into tight side-toside interengagement and todraw the head 20 of each terminal tightly against the underside of theresistor sheet 15 and the plural windings 18 at each hole 16. Thepressure tends to flatten each dished washer 30, as seen in FIG. 2, sothat metal margining the hole in each dished washer bites into thethreads of a respective terminal shank to maintain this sub-assembly.

The mica plate 14 may then be placed within the channel and thesub-assembly above described placed over the mica plate 14 and lined uplengthwise therewith. Thereafter, the channel sides 12--12 may be bentover the cover plate 25 and the assembly is completed. The washers 31may then be disposed over the extending ends of the terminal shanks 21and the nuts 32 threaded onto the latter.

The resultant assembly provides an electric heater of a lower profilethan that of the prior art heater shown in FIG. 4. In such prior artheater, a metal channel 10a is required, but of a greater depth than thechannel 10. Also required is a lower mica plate 14a, a resistor plate15a, an upper mica plate 23a and a metal cover plate 25a. The sides 12awere also bent over the cover plate, as in the improved construction.

Heretofore, the terminals 19a were quite different in that anintermediate portion had a shoulder and the lower end was formed tubularand longitudinally split at a plurality of places. The lower end of eachterminal was passed through a respective end hole in the resistor plate15a so that the shoulder 35 abutted against the upper surface of theresistor plate and the plural windings 18a. A Belleville washer 36 wasinserted over the lower end of each terminal, and such lower end wasthen deformed by a pressing operation to upset the longitudinally splitportions in rose-pedal manner, as seen at 37. i

It will be noted that the sub-assembly thus formed only of the terminalswound a and the resistor plate 15a. Therefore, the mica plate 23a, coverplate'25a, mica washers 27a and 28a and metal washers 29a constitutedloose parts which had to be added to the sub-assembly of the mica plateand terminals.

In contrast, my invention provides a sub-assembly including theterminals 19, the resistor plate 15, the mica plate 23, the cover plate25, the mica washers 27 and 28, and the metal washers 29, all heldtightly together by the deformed dished washers 30, and with theterminals held against rotation. It'will be appreciated that thissub-assembly may be more efficiently-manufactured. Additionally, theneed for the Belleville washer 36 (to hold the terminals againstrotation) is eliminated. v

A further advantage of my invention resides in the fact-that thedeformed dished washers tightly hold all parts of the sub-assembly inside-to-side relation, with only the smooth flat head 20 of theterminalsextending from the underside of the resistor plate 15a. In the prior artconstruction shown in FIG. 4, when the sides l2a12a were pressed overthe cover plate 25a, the legs of the rose-pedal 37 had a tendency to diginto the mica plate 14a and fracture or puncture the latter. This willbe more fully appreciated when it is understood that the plates 14, 15and 23 are insubstantial interengagement on final assembly in thechannel, rather than the spaced relation shown in FIGS. 2 and 4. Thus,any puncture or fracture of the mica plate could lead to dangerousshorting of the heating element, a condition which is avoided by thesmooth, flat heads 20 of the terminals 19.

I claim:

1. A strip heater assembly, comprising:

a sheet metal channel providing a base and upstanding sides, a firstsheet of insulating material within said channel and having one sidesurface bearing flatwise against the inner surface of said base, saidsheet being of a width substantially equal to the inner distance betweenchannel sides and of a length to overlie a major portion of the lengthof said inside surface,

a second sheet of insulating material of a width less than the width ofsaidfirst sheet, said second sheet having a hole at each end,

a resistor wound around said second sheet and having each ot its endswould between the margin of a respective hole and the adjoining side ofsaid second sheet,

a pair of terminal members, "each having a flat head and a shank, eachterminal member having its shank passing through a hole in said secondsheet and in contact with a resistor end portion in said hole, andhaving its head extending from a side surface of said second sheet andin contact with a resistor end portion adjoining said hole,

a third sheet of insulating material of a size generally equal to thatof said first sheet and adapted to overliethe opposite sidesurface ofsaid second sheet and the resistor wound thereover, said third sheethaving a hole at each end corresponding to the holes in said secondsheet and through which the shank of a terminal passes to hold saidsecond and third sheets in predetermined alignment wherein oppositelongitudinal portions of said third sheet overhang the correspondingmargins of said second sheet, 1

a sheet metal cover plate of a size generally equal to that of saidthird sheet, saidcover plate having a hole at each end, slightly largerthan the holes in said third sheet and through which the shank of aterminal passes in an electrically insulated manner,

electrically insulated securing means connected to each terminal shankand pressingagainst the adjacent surface of the cover plate to provide asubassembly comprising said second and third sheets and said cover plateheld tightly together in faceto-face relation between said securingmeans and the heads of said terminal members, said sub-assembly beingdisposedwithin said channel with said flat terminal heads bearingagainst theopposite side surface of said first insulating sheet, thesides of said channel being bent over said cover plate to firmly holdsaid sub-assembly within said channel. I l 2. The assembly according toclaim 1, wherein said securing means comprises a dished, metal washerhaving a hole to closely pass a respective terminal shank and aninsulating member interposed between the cover plate and the washer.

3. The construction according to claim 2 wherein further including a nutthreaded on each terminal each of said terminal shanks is threaded, andwherein shank outwardly of said cover plate for securing an the marginalsurface defining the washer hole tightly electrical conductor to ashank. interengages with the threads on said shank; and

1. A strip heater assembly, comprising: a sheet metal channel providing a base and upstanding sides, a first sheet of insulating material within said channel and having one side surface bearing flatwise against the inner surface of said base, said sheet being of a width substantially equal to the inner distance between channel sides and of a length to overlie a major portion of the length of said inside surface, a second sheet of insulating material of a width less than the width of said first sheet, said second sheet having a hole at each end, a resistor wound around said second sheet and having each ot its ends would between the margin of a respective hole and the adjoining side of said second sheet, a pair of terminal members, each having a flat head and a shank, each terminal member having its shank passing through a hole in said second sheet and in contact with a resistor end portion in said hole, and having its head extending from a side surface of said second sheet and in contact with a resistor end portion adjoining said hole, a third sheet of insulating material of a size generally equal to that of said first sheet and adapted to overlie the opposite side surface of said second sheet and the resistor wound thereover, said third sheet having a hole at each end corresponding to the holes in said second sheet and through which the shank of a terminal passes to hold said second and third sheets in predetermined alignment wherein opposite longitudinal portions of said third sheet overhang the corresponding margins of said second sheet, a sheet metal cover plate of a size generally equal to that of said third sheet, said cover plate having a hole at each end slightly larger than the holes in said third sheet and through which the shank of a terminal passes in an electrically insulated manner, electrically insulated securing means connected to each terminal shank and pressing against the adjacent surface of the cover plate to provide a sub-assembly comprising said second and third sheets and said cover plate held tightly together in face-to-face relation between said securing means and the heads of said terminal members, said sub-assembly being disposed within said channel with said flat terminal heads bearing against the opposite side surface of said first insulating sheet, the sides of said channel being bent over said cover plate to firmly hold said sub-assembly within said channel.
 2. The assembly according to claim 1, wherein said securing means comprises a dished, metal washer having a hole to closely pass a respective terminal shank and an insulating member interposed between the cover plate and the washer.
 3. The construction according to claim 2 wherein each of said terminal shanks is threaded, and wherein the marginal surface defining the washer hole tightly interengages with the threads on said shank; and further including a nut threaded on each terminal shank outwardly of said cover plate for securing an electrical conductor to a shank. 